flutter 等待条件满足，然后再继续执行其余代码

Question

在继续其余代码之前，我需要异步函数等待某些表达式验证(例如x == true)。

现在我正在像这样使用while循环

var x = false;

someFunction() async {

   // here I want to await for 
   // as long as it takes for x to become true

   while(!x) {
       await new Future.delayed(new Duration(milliseconds: 250));
   }

   // i put 250 millisecond intentional delay 
   // to protect process from blocking.
   // x is to be set true by external function
   // rest of code ...
}

await someFunction();

您是否认为有更好的方法等待x更改为true才能继续执行？
谢谢

Answer 1

您可以使用三种方式进行异步/等待:-

void method1(){
  List<String> myArray = <String>['a','b','c'];
  print('before loop');
  myArray.forEach((String value) async {
    await delayedPrint(value);
  });  
  print('end of loop');
}

void method2() async {
  List<String> myArray = <String>['a','b','c'];
  print('before loop');
  for(int i=0; i<myArray.length; i++) {
    await delayedPrint(myArray[i]);
  }
  print('end of loop');
}

Future<void> delayedPrint(String value) async {
  await Future.delayed(Duration(seconds: 1));
  print('delayedPrint: $value');
}